An HPLC-UV method for the simultaneous quantification of vemurafenib and erlotinib in plasma from cancer patients

• This study describes a sensitive and precise HPLC-UV assay for vemurafenib in plasma.
• This assay allows the simultaneous determination of erlotinib.
• Plasma concentrations of vemurafenib and erlotinib were assayed in cancer patients.
• The assay is applicable for the therapeutic drug monitoring in clinical settings.

Vemurafenib and erlotinib are two oral kinase inhibitors approved for the treatment of metastatic melanoma and advanced non-small cell lung cancer, respectively. In contrast with erlotinib, the single published method for analysis of vemurafenib in human plasma is based on mass spectrometry. The purpose of the present study was to develop an HPLC-UV method to simultaneously quantify these two drugs in plasma. Following liquid–liquid extraction, vemurafenib, erlotinib and sorafenib (internal standard) were separated isocratically on a C8 Xterra® MS using a mobile phase of glycine buffer (pH 9.0, 100 mM)/acetonitrile (45:55, v/v). Samples were eluted at a flow rate of 0.9 mL/min throughout the 12-min run. Dual UV wavelength mode was used, with vemurafenib and sorafenib monitored at 249 nm, and erlotinib at 331 nm. The calibration was linear in the range 1.25–100 mg/L and 50–4000 μg/L for vemurafenib and erlotinib, respectively. Inter- and intra-day precision was less than 6.7% and 6.6% for vemurafenib and erlotinib, respectively. This analytical method was successfully applied to assess the steady state plasma exposure of these drugs in cancer patients. This accurate method can be used in routine clinical practice to monitor vemurafenib or erlotinib concentrations in plasma from cancer patients.